don't reuse needles. the most common side effect is low blood sugar, which may cause dizziness, sweating, confusion, and headache. check your blood sugar. low blood sugar can be serious and may be life-threatening. injection site reactions may occur. tell your doctor about all medicines you take and all your medical conditions. taking tzds with insulins, like tresiba?, may cause serious side effects like heart failure. your insulin dose shouldn't be changed without asking your doctor. get medical help right away if you have trouble breathing... fast heartbeat, extreme drowsiness, swelling of your face, tongue, or throat, ask your doctor if you're tresiba? ready.